


In Heat

by aspentgladiator



Category: Undertale (Video Game)
Genre: F/M, Undertail
Language: English
Status: In-Progress
Published: 2015-11-30
Updated: 2016-02-03
Packaged: 2018-05-04 04:26:22
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 4,356
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5320403
Author URL: https://archiveofourown.org/users/aspentgladiator/pseuds/aspentgladiator
Summary: <blockquote class="userstuff">
              <p>Your friend always says there are no hot guys around their favorite hangout. You're inclined to disagree. Welcome to Grillby's.</p>
            </blockquote>





	1. In Heat

**Author's Note:**

> This fic is intended to be a slow burn romance/smut fic between Grillby and a cis female reader. Just an idea I've had rolling around, but the first chapter isn't getting to the best bits. Just a taste for now. Enjoy!

It’s been two months since monsters had arrived on the surface, and while you still weren’t used to it, you thought everyone that had come up was pretty cool. They had advocates, celebrities, and their own culture that they brought to the surface. And while they weren’t exactly used to not having a monarchy rule over all the land, they easily made friends with the humans who accepted them. Some, unfortunately, were not so welcoming, but you were not among them. 

You’d made a friend, a funny bunny who’d lived in a town below the surface called “Snowdin” before the monsters were set free, They were friendly, and loved to go out with you, but was oddly homesick at times. Their main hangout back home, Grillby’s, had closed soon after the barrier had been destroyed, and even though they had complained about it being the only place to go back when they’d lived in Snowdin, they had a missed hitting on their “skeleton friend” and downing bottle after bottle of ketchup in solitude. You often shrugged your shoulders at the notion. You had taken them to surface clubs when you had the chance, but they seemed uninterested in most human men, and they hated the taste of the drinks they served.

So when you heard that a new Grillby’s was opening up in just a few days, you had to be the first to tell them.

[text] so guess where we’re going thursday night?

[text] funbun<3: GRILLBY’S omg sans invited us both to the grand opening!!!!!! can you believe it???? omg i can’t wait there are going to be soooooooo many hot guys <3 <3 <3

You rolled your eyes at your phone. Of course they already knew. They were always one step ahead of you. You got up and looked in your closet. Most of what you had was casual, comfortable...not too much made for clubbing. Besides, from what Funbun had told you, Grillby’s was something of a dive bar in Snowdin. How different could it be? You decide not to worry about what to wear for now. It’s not for a few nights, so you decide to focus on other things until then.

~

Classes the night of Grillby’s had wrecked you; your brain was fried and you couldn’t wait to unwind. Funbun was at your apartment just minute after you got home, and you got ready together. They were wearing a sparkling crop top and a short black skirt that hugged their body, something they normally wore when you took them out to clubs the few times you had gone.

“What should I wear?” You ask them.

“Oh jeez, ummm...” Funbun opened up your closet, running a finger along your hangers and sighing. “Maybe just, I dunno, wear whatever you feel best in.”

You settled on a dark pair of jeans and a plain tshirt. Funbun sighed again at you, but then cracked a smile. They knew it just wouldn’t be like you to get too dolled up.

~

Grillby’s turned out to be a lot different from what you imagined. Your taxi pulled up, and a sign that displayed the establishment’s name appeared to be written in flames against the brick exterior. It was shockingly trendy, and while there were a line of humans out the door, monsters and their companions appeared to be able to easily skip it and get inside. Aside from the rabble of people outside, it was oddly quiet. Normally when you’d waited outside of clubs before, the music was so loud you could feel the bass in your chest. But when you walked inside, music trickled out from a jukebox in a corner, everyone seemingly ignoring it while they stood around and mingled. A few humans were inside, but you felt so small around so many monsters. Your arm tightened around Funbun’s and they put a hand on yours. 

“You’re fine. OMG Sans!!!!!!!!” Funbun immediately left your side and picked a short, pudgy skeleton off of the ground, squeezing him tight against their chest before setting him down. This was the monster king’s righthand man? A skeleton in a hoodie and slippers?

“Yeah, and you’re a frumpy looking human who is looking pretty under-dressed for the occasion. What’s the problem, have trouble catching up with your friend here?” As if on queue, he pulled a ketchup bottle out from behind him and took a deep swig. You could have sworn that wasn’t in his hand before, but you choose not to question it. Sans is, rumor has it, the most powerful monster in the world. You chuckle to yourself and look away, his empty eye sockets burning into yours somehow, and you find your way up to the bar. Funbun is happier than you’ve seen them in weeks, and it makes you smile. A human guy makes eyes at your from across the bar, but you aren’t interested. You feel exposed, uneasy, and a bit unwelcome.

But as you stared into the phone sitting in your lap, knowing that not a single notification was due to light up your screen no matter how long you stare, a wave of heat washed over you. It was so strong you felt beads of sweat starting to form on your brow. And when you looked up, you had to squint for a second before you realized what you were looking at. The figure was a masculine shape made entirely of fire, cleaning the inside of a scotch glass with a white cloth. The glasses on his face appeared to cling to the shape of a nose, and as the light changed when he moved, you could see different features being defined. His clothes clung to his form, suspenders digging into what appeared to be muscular shoulders, but that couldn’t be, because, well, fire. You were perplexed, intrigued, and, against your better judgement, you couldn’t stop looking. You couldn’t comprehend how such a creature could exist, and that was saying something, since you’d seen quite a lot of monsters in the past few months.

“And your friend always complains there are no hot guys here.” You almost jump out of your skin at the sound of Sans’s voice beside you. He’d slid into the seat next to you, much to the chagrin of the guy that had been eyeing you, and was chuckling deeply. “Grillby!” The fiery gentleman turned to look at Sans and walked over so gently, he appeared to just drift from side to side. “Can you get a good burger for my new pal here?”

“Well you’re just pals with everyone, aren’t you?” You sighed and watched Grillby head into the back. “Why is this place so popular? It kinda seems like...”

“What, a little too burnt out for ya?” Sans popped open the ketchup bottle with one finger and gulped out of it, the red sauce sliding out of the sides of his mouth. He wiped his hand on his sleeve. “Yeah, I’m friends with everyone. But that’s the advantage of being a strong monster. I’m stronger than all the humans. I’m stronger than everyone. I could probably kill you in about...5 minutes.” Sans laughed coldly. “But I won’t. Not anymore. I’m glad it’s...over.”

You were still a little lacking in your monster history, but you understood the gist of it. Sans you’d only heard of until tonight, but he was a legend.

“So you just...come here and hang out with us...common people? And monsters, and monsters,” you add. Before he could answer Grillby had brought out their burgers, and the heat wave washed over you again. This time it felt more comfortable, like a sitting beside a fire. Which you were. You still weren’t used to it.

“Hey Grillbz, take care of my new friend here.” Sans shoved the ketchup bottle into his pocket and hopped off of the bar stool. “Seems she has a lot of catching up to do.”

“You already made that joke!” You shout after him. A deep, warm chuckle escapes the figure standing next to you, and you feel something hot pool inside your chest. You turn to him and smile.

“So, uh,” you poke your burger with a fork, not feeling very hungry and just realizing that Sans had left his behind. “Does he come here often?”

Grillby nodded.

“Do you?”

Grillby nodded.

“Do you...wanna tell me more about what life was like underground? Before?”

Grillby considered for a moment, and then nodded. You squint at him curiously.

“Are you gonna tell me now or...just keep nodding?” 

He smirked just slightly, and in a smooth voice, that was deep but gently so, he simply said “Later.”

Something about the way he carried himself kept your attention. He didn’t have to say anything. He didn’t have to do anything significant. You could watch him wipe that already clean scotch glass all night. You weren’t even sure they served scotch there.

~

You had hardly spoken a word to anyone all night. Funbun had approached you once in an attempt to tug you off of your posted up spot at the bar stool next to the two cold burgers from earlier that night, but failed to move you very far and gave up after a few seconds. That was normal for them. You’d go out together, Funbun would tear it up, and you’d just relax and wait. But normally on these nights you’d drink a little, eat, and maybe talk to the people around you. But you’d spent all night watching Grillby move to and fro. He brought out bottles of ketchup to people, would go in the back to cook burgers and fries (all perfectly cooked, surprisingly never burnt), and went back to wiping things down with his towel. Every monster present seemed to know him, and yet he would never exchange words. His expression would change ever so slightly, and he would nod or shake his head, but the only words you’d heard come out of his mouth were directed at you. He drifted and floated behind the bar, so graceful and quiet, and yet so strong. It was captivating. “Later," is what he'd said. "Later."


	2. Maybe Later

**Summary for the Chapter:**

> A little bit of mystery to keep you on your toes for what's ahead. Big things!~

Finally, it was Later. The night had died down slowly, monsters seemed to be able to party as long as they wished without tiring, but they all had places they wanted to be. You, however, had the weekend off, and hadn’t been assigned a bedtime in over ten years. So when you peeled yourself off of your bar stool to walk a slightly intoxicated Funbun outside (ketchup did weird things to monsters), you were surprised to find that you actually felt less lonely now that it was just you and this great ball of fire behind the bar. 

When you walked back inside, happy to be back in the warmth, Grillby was sitting in one of the booths with what looked like a bottle of scotch and a glass. You took the seat across from him, and spotted a grin materialize across his face. He lifted another glass from the seat beside him, set it next to its twin, and splashed the drink into the glasses. You didn’t drink much, but you figured it might be rude. This was his bar, after all. You watch him down the liquid in his glass in a single gulp, the fire that twirled at the top of his head growing brighter. The booth felt that much hotter as you quickly tossed back the shot, shivering as you did. It tasted of cough medicine, and burned your throat. It came from a bottle, but it felt like hot chocolate going down. Grillby chuckled. You blushed.

“So…about the history lesson.”

“Later.” Grillby poured more of the drink into his own glass and swirled it around a bit, staring into it. You fidgeted in your seat a little bit. Wasn’t this later? You’d waited around a few hours, there was no one else around. How hard could it be to tell a little history. “Drink?”

“No thanks. So…” you laced your fingers together and twiddled your thumbs together a little. “How are you liking the surface?”

“Different,” he stared into his glass as if it were a million miles deep before taking more in, the heat emanating from him intensifying. His finger traced the rim of the glass and you couldn’t take your eyes away from his hands. They were defined, and strong, and flecks of flame floated away from his knuckles and fingertips. Without a second thought, you reach out to touch him. His hand recoils, and apologies are immediately pouring out of your mouth.

“Oh my god, I’m so sorry, I’m so stupid I didn’t meant to offend, I-” All this time, Grillby was shaking his head and holding his hands up. You quieted down, and he smiled at you, a light chuckle escaping him. It made you feel safe. But you wouldn’t be reaching towards him again any time soon. The warmth in the booth was like that of a warm blanket now, comforting and homey. “So what is the most different?” You hold your hands in your lap, gripping your fingers and still feeling a bit nervous.

He leaned back in the booth and folded his arms behind his head. He looked relaxed, and as his shirt tightened against his torso, you noticed how muscular he appeared to be underneath all that fire. His rolled up sleeves strained against his arms, the flames harmlessly licking the cushions of the booth. With a deep breath, he finally answered. "The sky." You realized you'd probably taken it for granted your whole life. Shooting stars, rainy days with clouds, the sun...it was all pretty commonplace. 

"Yeah, humans and monsters aren't all that different," you smiled at the man on fire across from you. He lowered his arms and you noticed his color turn slightly more pink than orange, even if it was for just a moment. "I mean, on the inside. Like, our souls must be the same." Grillby shook his head and stood up, taking the scotch glasses with him. He walked in the back and you stood and waited, praying you hadn't offended him. Monsters had faced a lot of oppression since their release, so how could she really understand what it meant to be one of them when she didn't even know their history? Luckily, Grillby returned moments later, motioning toward the front door of the bar. 

"Um, do you have paper? And a pen?" He tilted his head to the side before going back to the bar, and grabbing a napkin, and bringing it to her along with the pen he kept in his pocket. You used the wall as a surface to scrawl your number into the napkin, along with a message to remind him that you expected a history lesson soon. 

Grillby gingerly held the napkin, and smiled. "Goodnight." 

"You too, Grillbz." 

When you stepped outside, the cold stung against your bare arms. You instantly missed being near Grillby, and even when you got into the heated cab, it just didn't do his presence justice. You texted Funbun when you got home safely, and instantly passed out once you wrap yourself in blankets, trying to simulate the warmth you felt. For a man, or monster, of few words, he was captivating. That night you dreamt in yellows and orange and reds.

~

In class you felt yourself nervous, and distracted. You barely listened to your professor, as they droned on in front of a sea of notebook computers and your sleep deprived classmates. You nervously messaged Funbun back and forth on Facebook as they interrogated you on every detail of your private time with Grillby. You weren’t about to admit that you wished it had lasted longer, but Funbun was no fool. They saw right through you, and their teasing was relentless. And as you walked home from class, you could feel the blush on your cheeks grow hotter with every teasing comment they made towards you. You were so distracted, you didn’t even notice the skeleton in the hoodie sitting on your couch when you walked in.

At first, you screamed, because you were startled, but as soon as you recognized Sans you calmed down. You contemplated asking him how he got in, but knew it probably had something to do with his “powers” that Funbun never shut up about.

“What are you doing here?”

“What do you humans watch on TV? You don’t even get the MTT channel up here.” Sans shook his head and patted the spot next to him. You felt strange being invited to sit on your own couch. You sat on the couch, your backpack still on, and your bottom on the very edge. You felt a strange sense of guilt worming around in your stomach.

“Okay, what are you-”

“Did you have a drink with Grillby last night?”

You grabbed your arm, blocking yourself off. The memories swirled in your brain, warm and welcoming. But nothing much had come of it, other than a promise of something to come later. The sense of guilt was briefly replaced with a warmth that pooled toward the bottom of your abdomen.

“I’ll take that as a yes. What did he tell you?”

“Just...just that things are different here. And he likes the sky. But probably not the rain.” You giggled at the thought. “And, uh, that he’d tell me more later.”

Sans shut his eyes and chuckled, leaning his head back. “Well kid, you’ve certainly sparked his interest.” He stood up off the couch and put his hands in his pockets. “Do you know what Determination is?” 

Your eyebrows raised curiously. “Um, I mean, sure. It’s like, the will to go on. And to fight. When you’re determined you’re...you’re willing to succeed no matter what. Something like that. Why?”

Sans shook his head. “Did you know that monsters don’t have such a thing as determination? Some do, but only in small amounts. When they die, they turn to dust. Some of us, some of our souls, can last for small moments after death, but soon we face the same fate,” Sans shuffled his slippers back and forth across your carpet. “Humans have...limitless amounts of determination. That’s all I’ll say for now. Just keep trying until ‘later’ comes, y’know? You’ll get there.And it’ll be...worth it when you do.” He headed towards the door, but you couldn't help before more confused than ever.

"Wait, what do you mean? What's so important about determination?" You barely kept yourself from demanding to know what Sans was hiding about Grillby and his behavior. What made it worse was that Sans just grinned mischievously at you, with one slippered foot holding the door open. 

“Just remember that when you play with fire, you take the risk of getting burned.”

**Notes for the Chapter:**

> Please leave comments/kudos to let me know what you think! Your comments on the first chapter filled me with DETERMINATION ;)


	3. Grillby's Back Room

**Summary for the Chapter:**

> It's finally later. You go back to Grillby's Bar and are taken on a little field trip...

Every night, the dreams continued, each one more vivid than the last. You’d wake up sweating, and hot. You remembered the flames trapping you, getting higher and hotter, but you were not afraid. You felt comfortable, and safe. The next week filled you with anticipation. The next time you’d see Sans would be when you and Funbun inevitably went to Grillby’s that Friday night. And when the night came, you found yourself more concerned with what to wear than the last time you’d visited. Funbun had definitely noticed.

“So are you suuuuure all you did was have a drink? Because I’ve never seen you act like this.”

“You’ve only known me a couple of months,” you reply, switching shirts in front of the mirror without putting them on yet. “He’s quiet. I don’t...know much about him yet. He’s cute, though.”

“Yeah I mean, he’s pretty hot if you ask me. Or anyone.”

Your blush intensifies, and you almost feel jealous for a moment until you understand their joke. “You’ve been spending too much time with Sans.”

Funbun blushed, and you can practically see their eyes forming into hearts. “Not enough time if you ask me. Come on and pick something! We’re gonna be late.”

~

You arrive at Grillby’s in a similar fashion as you did the week before, only this time in a flashy mini skirt and blouse that you’d found hidden at the back of your closet. You almost felt like the heels were too much, but you’d probably sitting on a bar stool most of the night anyway. As soon as you enter, Funbun seems to get swallowed up by the crowd, which is as big and diverse as it was last week, though you swear you see a few more humans as you squeeze towards the bar.

Grillby notices you almost immediately, and you notice his flame grow visibly brighter and more red than orange. Once he finishes helping the customer he was with, he glides over to you, his warmth enveloping you. You think about the first time you were here, and how the heat was uncomfortable. Now it reminds you of comfort, of hot cocoa or a blanket. You smile at him, and notice his cheeks turn up ever so slightly as well. He pours you a drink, more of the scotch-like stuff you’d tried the other night. You brace yourself as you down the liquid quickly, the burning in your throat even feeling more familiar than it had before. He watches you intently as you drink every last drop, and you accept when he silently offers you more. Most of the night you simply swirl the drink around in the glass and watch him work. The liquor smells like smoke and emits its own warmth. It reminds you of Grillby himself.

~

At the end of the night, you lean with your back to the bar as patrons stumble out. You ask Funbun if they need company on the way home, but you both know where you’d rather be tonight. They kiss you on the cheek and leave, practically skipping out of the bar. You know you’ll have to text them later about the rest of the night. “Speaking of later...” you think to yourself.

The bar is finally empty, your bottom is sore from being basically glued to your seat all night, and Grillby is still in the back. You look around guiltily before walking behind the bar and cautiously opening up the door to the back.

It looks like a storeroom. There are shelves of ketchup and alcohol, as well as a sink and a place for dishes beside it. Past the rows of shelves, there is a door open, and a warm light emitting from the inside. Your curiosity gets the best of you, and when you round the corner to enter the door, Grillby is standing just inches from the doorway. You gasp, and he puts a finger up to your lips. It almost feels hot enough to burn, but not quite. He pulls a large coat from behind his back and hands it to you.

“What’s this for?” You ask.

“Later,” he replies. You notice a flight of stairs behind him as you slip into the coat. As soon as you zip the coat up, he starts walking. Grillby is the only light source, and you lose sight of the light from the back of the bar. No light source is coming from the bottom of the steps, at least not yet.

“Where are we going?” You probe, getting colder the further down you go. When your legs rub together you can feel the goosebumps forming on your thighs.

“Home,” Grillby says before stopping suddenly. He put his hand flat against a solid wall in front of him made of stone, and you watched it melt away into nothingness and then you were...in the same room as before. Rows of ketchup and liquor, the sink with the dishes, the door back out to the bar...

“Okay, good trick.” You chuckle and your teeth chatter, and you feel your knees knock together from the cold again. “Why is it so damn cold in here now?” Grillby grins back at you in a way you haven’t seen before. He looks mischievous, and you feel your heart start pounding out of your chest. He walks back into the bar, but you feel frozen in place. You can’t tell if that feeling is fear or excitement, or maybe a cocktail of both. With a deep breath, you follow Grillby back into the bar. He looks right at home, cleaning the inside of a glass with a rag. He was beaming with pride around the empty, slightly dusty bar. This was not the same place you were earlier tonight.

“Drink,” Grillby had poured a glass of the scotch-like drink for you and set it on the counter. He even poured one for himself this time, and you clinked your glass with his, grinning nervously.

“To...new adventures. And to finally getting around to Later.” As you finish your toast, Grillby gives you the same smirk from earlier. The drink does little to warm more than your throat, but at least now your teeth had stopped chattering. If only Grillby had given you some leggings. When he downed his drink, his flame grew brighter and redder. You swear he 

“Still cold?” He steps closer to you, and you press your back to the bar. His flame is hotter than it had been earlier, or maybe he's just closer than he was before. “Want some help?”

You can feel the warmth burning in your cheeks, unsure if you’re blushing or absorbing Grillby’s heat as he gets ever closer to you. He opens his mouth wide, the inside dripping like hot magma as a long tongue lolls out past his chin. Your heart is pounding out of your chest and you close your eyes as his hot, wet tongue makes contact with your cool skin. It feels hot enough to burn, like molten wax running all along your neck as he makes his way. His tongue makes its way to your jawline, and he growls in your ear.

“Shall I continue?”

**Notes for the Chapter:**

> it's been a while since i updated! i was pretty distracted over the holiday but i was glad to finally get back to writing this. next chapter should be up pretty soon, since i got pretty into writing this one ;)
> 
> leave your comments! they really motivated me to get working on this again even sooner and filled me with DETERMINATION!!! <3
> 
> edit: I have an Undertail tumblr! I reblog a lot of different ships and link to new chapters there. Follow it @tsundertail


End file.
